1. Field of the Invention
The present invention relates to a method of generating and a system of generating an exposure pattern for a lithography process used for semiconductors, liquid crystal substrates and printed boards, and more particularly to an exposure pattern generation method and an exposure pattern generation system which allows creating micro-patterns by a low technology stepper machine, such as an i-line, using a plurality of reticles or mask substrates.
2. Description of the Related Art
As the size of semiconductor devices decreases and precision thereof increases, micro-patterns must be created on a wafer at a required precision to satisfy the device characteristics. Therefore a reduction in size and an increase in precision are demanded for a photo mask (hereafter reticle) used in the wafer exposure process as well. Methods to create micro-patterns on a wafer at high precision are diversifying, and the price of reticles and the cost of aligners are increasing accordingly.
As a method of creating conventional micro-patterns (e.g. a 200 nm or less design rule), performing OPC processing (Optical Proximity Correction), where the exposure pattern is corrected considering the proximity exposure effect when the design data is converted to the format of the electron beam aligner to create exposure pattern data, and generating patterns by a stepper machine with a KrF excimer laser beam (248 nm) or an ArF excimer laser beam (193 nm) using a phase shift mask, have been proposed.
However, such conventional methods are not sufficient solutions since the data processing for OPC processing takes time, the cost of phase shift masks is high, and a stepper machine with a KrF or ArF excimer laser beam must be newly installed.
As a lithography method which allows the generation of micro-patterns using a conventionally popular i-line (365 nm) stepper machine, creating micro-patterns by a plurality of times of the lithography steps using a plurality of (e.g. two) reticles, has been proposed. For example, xe2x80x9cwavelength-independent optical lithographyxe2x80x9d in J. Vac. Sci, Technol. B 18 (1), January/February 2000, discloses creating micro-patterns, executing exposure, developing and etching twice using two reticles, and creating micro-patterns by the composite pattern of these two reticles.
FIGS. 1A to 1C are diagrams depicting a conventional general lithography step. This lithography step comprises an exposure process (FIG. 1A) where light hv is irradiated onto a resist layer 4 coated on the patterning target layer 3 of the wafer substrate 2 using the reticle 1 which has the light transmission hole Pa, a resist development step (FIG. 1B), and an etching step using the resist as a mask (FIG. 1C). When the light transmission hole Pa becomes very small, the resist 4 cannot be developed to be a shape with the same pattern width a1 as the light transmission hole Pa. This is because light is out-of-focus, and resist cannot be finely processed by a stepper using such a long wavelength light as an i-line. As a result, the final pattern 6 to be created on the patterning target layer 3 tends to have a pattern width smaller than the pattern width a1 of the reticle 1.
FIGS. 2A to 2F are diagrams depicting the wavelength-independent lithography step which is proposed by the above mentioned article. In this lithography step, exposure, development and etching are performing with a reticle A, which has a pattern Paa when a micro-pattern Pa is enlarged in a first direction, and a reticle B, which has a pattern Pab when the micro-pattern Pa is enlarged in a second direction respectively, so that the micro-pattern Pa is created by a composite of the reticles A and B. In exposure using the reticle 1 having the micro-pattern Pa, the resist cannot be patterned accurately because the long wavelength light, such as visible light, is out-of-focus, but in the case of exposure using the reticles A and B, which have patterns when the micro-pattern Pa is enlarged respectively, the resist can be patterned accurately even with long wavelength light.
As FIG. 2A shows, a protective layer 10, such as oxide film, and a resist 4A, are created on the pattern target layer 3 on the wafer 2, and in the first exposure, the first reticle 1A, which has a pattern Paa when the processing target pattern Pa is enlarged to the upper left direction, is used for exposure (FIG. 2A). And this resist 4A is developed and the resist 4A is patterned. Since the transmission hole Paa is not a micro-pattern, light does not become out-of-focus during exposure, and the pattern Paa can be transferred onto the resist 4A accurately. The protective layer 10 is etched using this resist 4A as a mask (FIG. 2C). The width b1 of the pattern created on the protective layer 10 is sufficiently larger than the width a1 of the processing target pattern Pa.
Then the resist 4B is created on the protective layer 10 again, and a second exposure is executed. In the second exposure, the second reticle 1B, which has a pattern Pab when the processing target pattern Pa is enlarged to the lower right direction, is used for exposure (FIG. 2D). When the resist 4B is developed and the resist 4B is patterned, the pattern becomes a pattern which partially overlaps with the pattern on the protective layer 10, created after the first exposure step (FIG. 2E). This pattern width b2 is also sufficiently larger than the width a1 of the processing target pattern PA. Finally, using the pattern of the protective layer 10 and the pattern of the resist 4B as a mask, the patterning target layer 3 is etched (FIG. 2F). As a result, the processing target pattern Pa is created on the patterning target layer 3 by a composite pattern, where the enlarged pattern Paa of the reticle 1A and the enlarged pattern Pab of the reticle 1B are overlapped.
FIGS. 3A and 3B are diagrams depicting the generation methods for two reticle patterns to be used for the lithography step shown in FIG. 2. As FIG. 3A shows, the pattern of the reticle A, which is the first reticle, is an enlarged pattern Paa, where the left edge and the top edge of the processing target pattern Pa are extended. And as FIG. 3B shows, the pattern of the reticle B, which is the second reticle, is an enlarged pattern Pab, where the right edge and the bottom edge of the processing target pattern Pa are extended. The composite pattern where the patterns Paa and Pab of the reticles A and B overlap becomes the processing target pattern Pa.
Exposure and development are executed using the two reticles which have enlarged patterns, so a micro-pattern can be created using an i-line-based low technology stepper machine. However, the exposure, development and etching steps must be executed twice.
FIGS. 4A to 4C are diagrams depicting a problem of the above mentioned lithography method. This example is the case when the above mentioned lithography method is applied to four micro-patterns Pa, Pb, Pc and Pd, which are longer in the longitudinal direction, wherein the patterns Pb and Pc, out of the four micro-patterns, are close to each other. In the case of a micro-pattern which is longer in the vertical direction, the pattern of the reticle A becomes the enlarged patterns Paa, Pba, Pca and Pda, where the left edges are extended, as shown in FIG. 4A, and the pattern of the reticle B becomes the enlarged patterns Pab, Pbb, Pcb and Pdb, where the right edges are extended, as shown in FIG. 4B.
In this case, the gray patterns where both patterns overlap in FIG. 4 become the processing target micro-patterns Pa, Pb, Pc and Pd, but since the patterns Pb and Pc are close to each other, the enlarged patterns Pca and Pbb of these patterns partially overlap, and the finally created patterns include the error pattern Px, which is created between the micro-patterns Pb and Pc, as FIG. 4C shows.
To prevent the generation of this error pattern Px, the degree of enlargement when the reticles A and B are created is decreased, but then, the enlarged patterns become similar to the original micro-patterns, and the pattern accuracy drops because light is out-of-focus during exposure.
FIGS. 5A and 5B are diagrams depicting another problem of the above mentioned lithography method. This example shows the case when an L-shaped micro-pattern is created. As FIG. 5A shows, the L-shaped micro-pattern is comprised of two rectangular patterns Pa and Pb. For these two rectangular patterns Pa and Pb, the reticle A, which has enlarged patterns Paa and Pba when the patterns Pa and Pb are extended to the upper left direction, and the reticle B, which has the enlarged patterns Pab and Pbb when the patterns Pa and Pb are extended to the lower right direction, are generated, and a composite pattern is generated by both reticles. The composite result is shown in FIG. 5B. In other words, the area where the enlarged pattern of the reticle A, shown by the solid line, and the enlarged pattern of the reticle B, shown by the dashed line, overlap (double exposure area), is created in the final pattern. A multiple exposure area is generated at the area Px, which the original micro-pattern does not have, which becomes the error pattern Px.
As described above, in the case of the method of creating a micro-pattern by multiple exposure using two enlarged patterns, a multiple exposure area is created in an unexpected area when the micro-patterns are close to each other, or when the micro-patterns are bent, such as in an L-shape, where an error pattern is created.
With the foregoing in view, it is an object of the present invention to provide an exposure pattern generation method and an exposure pattern generation system for lithography which can solve the above problems and prevent the generation of an unexpected multiple exposure area.
To achieve the above object, the first aspect of the present invention is a method of generating an exposure pattern for lithography to create a plurality of patterns arranged in a predetermined direction, comprising a step of counting the plurality of patterns along this predetermined direction, and generating a first enlarged pattern by moving the edges to a first direction along the predetermined direction for a pattern with an odd number, and by moving the edges to a second direction, which is opposite to the first direction, for a pattern with an even number, and a step of generating a second enlarged pattern by moving the edges to the second direction for the pattern with an odd number, and by moving the edges to the first direction for the pattern with an even number. And the first and second patterns are used for creating the plurality of original patterns in a lithography step using the respective enlarged patterns.
In this method, the direction of moving the edges of adjacent patterns for generating an enlarged pattern is opposite from each other. By this, overlapping of the first enlarged pattern and the second enlarged pattern in an area, which the original pattern does not have, is prevented, and therefore the generation of an error pattern is prevented.
To achieve the above object, the second aspect of the present invention is a method of generating an exposure pattern for lithography to create an L-shaped pattern combined by a plurality of rectangular patterns, comprising a step of generating a first enlarged pattern by moving the edges of the L-shaped pattern to the external angle direction of the L-shaped pattern, and a step of generating a second enlarged pattern by moving the above mentioned edges to the internal angle direction of the L-shaped pattern. The first and second enlarged patterns are used for creating an original L-shaped pattern in the lithography processing using the respective enlarged patterns.
According to this method, in the case of the L-shaped pattern, which is bent and has an internal angle and an external angle, the direction of moving the edges of the plurality of rectangular patterns constituting the L-shaped pattern is the external angle direction for the first enlarged pattern, and the internal angle direction for the second enlarged pattern. As a result, a multiple exposure area where the first and second enlarged patterns overlap will not be produced in any place but in the original L-shaped pattern.
To achieve the above object, the third aspect of the present invention is a method of generating an exposure pattern for lithography to create a cross-pattern, such a cross-shaped pattern, comprising a step of separating the cross-pattern into an L-shaped pattern and a rectangular pattern, a step of generating a first enlarged pattern by moving the edges of the L-shaped pattern to the external angle direction, and moving the edges of another rectangular pattern connected to the L-shaped pattern to a direction the opposite of the external angle direction, and a step of generating a second enlarged pattern by moving the edges of the L-shaped pattern to the internal angle direction, and moving the edges of another rectangular pattern connected to the L-shaped pattern to a direction the opposite of the internal direction. And the first and second enlarged patterns are used for creating an original cross-pattern in the lithography step using the respective enlarged patterns.
According to this method, an error pattern is not generated for the L-shaped pattern, and also the direction of moving the edges of the rectangular pattern, which is adjacent to the L-shaped pattern and forms the internal angle and the external angle with the L-shaped pattern, is set to a direction the opposite of the direction of moving the edges of the L-shaped pattern, so the generation of an error pattern at a position crossing the L-shaped pattern and the rectangular pattern is prevented.
To achieve the above object, a fourth aspect of the present invention is a method of generating an exposure pattern for lithography to create a plurality of patterns, comprising a step of generating a first enlarged pattern by moving the edges of the original pattern to a first direction, a step of generating a second enlarged pattern by moving the edges of the original pattern to a second direction which is the opposite of the first direction, an AND processing step of executing AND processing of the first and second enlarged patterns and generating an AND pattern having an area where both the enlarged patterns overlap, an exclusive processing step of executing an exclusive OR processing of the original pattern and the AND pattern, and generating an exclusive pattern having an exclusive area of the original pattern and the AND pattern, and a removal processing step of generating a new first enlarged pattern by removing the exclusive pattern from the first enlarged pattern.
According to the above method, even if a multiple exposure area, which the original pattern does not have, is generated by the lithography method using the first and second enlarged patterns, the generation of an incorrect multiple exposure area is prevented by predicting such a multiple exposure area, and removing the area from the first or second enlarged patterns.